Skip delete_at_update for replication requests

Requests through the object server that are from backend replication
should not send x-delete-at updates to the .expiring_objects account.
Replication is just moving data around or making new replicas, not
creating new data from nothing.

Change-Id: I324864face3ff559822c7a50c50e675e8b889b48
Merge "Skip delete_at_update for replication requests"